In recent years, more photovoltaic power generation systems have been built for effective use of renewable energy. This has increased the number of reports on fire accidents caused by arc faults in such photovoltaic power generation systems.
When an arc is generated in a photovoltaic power generation system, the circuits need to be shut down rapidly to prevent fire from the arc. The photovoltaic power generation system may need rapid shutdown of its circuits in response to an arc, and thus may include an arc detector.
An arc, either a serial arc or a parallel arc, generated in a photovoltaic power generation system including solar cell strings connected to a power conditioner causes noise. An output line of each solar cell string outputs a signal containing noise from the arc superimposed on the switching noise from the power conditioner. Thus, the arc detector obtains a signal from an output line and obtains an arc signal from the obtained signal to detect an arc.
This type of arc detector may have a known structure shown in Patent Literature 1 or 2. The arc detector described in Patent Literature 1, which is included in a photovoltaic power generation system connected to a power conditioner, detects an arc with the processing described below. The arc detector first detects a current flowing through the photovoltaic power generation system, determines the power spectrum of the detected current, and divides the power spectrum into multiple bands. The arc detector then filters one or more interference signals (noise) generated from the power conditioner from the power spectrum within those separate bands, and detects an electrical arc in the high-voltage system using the remaining signals within each band, which are other than the interference signals. When filtering the interference signals, the arc detector identifies one or more peak values in one or more frequency bands, and at least partially narrows the power spectrum of each of these frequency bands. In other words, the arc detector in Patent Literature 1 detects an arc without using the preset frequency band of interference signals generated from the power conditioner, and detects an arc by narrowing the power spectrum of the preset frequency band of the interference signals.
The arc detector described in Patent Literature 2 detects an arc using the power spectrum of a voltage, instead of using the power spectrum of a current flowing through an output line of a solar cell string, because noise in accordance with the magnitude of an arc is superimposed on the switching noise of the power conditioner. More specifically, this arc detector detects the voltage from the output line of the solar cell string using a voltage sensor, determines the power spectrum of the voltage based on the detected voltage, and detects an arc based on the determined power spectrum. In this case, the frequency band of the switching noise from the power conditioner is specified. The power spectrum of the specified frequency band is excluded from the target for arc detection, whereas the power spectrum of the remaining frequency band is used to detect an arc.